Bug 1850295 - Update :user-{valid,invalid} to follow the spec. r=smaug

(Modulo open spec issues linked in comments)

Differential Revision: https://phabricator.services.mozilla.com/D196986

dom/html/nsGenericHTMLElement.cpp

@@ -1795,7 +1795,6 @@ void nsGenericHTMLFormElement::ClearForm(bool aRemoveFromForm,
   UnsetFlags(ADDED_TO_FORM);
   SetFormInternal(nullptr, false);
   AfterClearForm(aUnbindOrDelete);
-  UpdateValidityElementStates(true);
 }
 
 nsresult nsGenericHTMLFormElement::BindToTree(BindContext& aContext,
@@ -2148,11 +2147,6 @@ void nsGenericHTMLFormElement::UpdateFormOwner(bool aBindToTree,
       form->AddElementToTable(this, idVal);
     }
   }
-
-  if (form != oldForm) {
-    // ui-valid / invalid depends on the form for some elements
-    UpdateValidityElementStates(true);
-  }
 }
 
 void nsGenericHTMLFormElement::UpdateFieldSet(bool aNotify) {